Radio beacon transmitter



L DUBIN RADIO BEACON TRANSMITTER Filed April 17, 1945 fllll Ill Il.

iv# w1 IN VEN TOR E6 TER DUB/N A TTORIVEY some previous systems.

atented July@ 1948 RADIO BEACON TRANSMITTER Lester Dubin, Brooklyn, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y.. a corporation of Delaware Application April 17, 1945, Serial No. 588.843

19 Claims.

'I'hls invention relates to signal combining and control circuits and more particularly to such circuits applied to radio beacon transmitters of the omnidirectional type.

The copending application of E. Labin and D. D. Grieg, Ser. No. 581,974, led March l0, 1945, discloses a beacon system which is applicable to various modulation methods wherein a directive radio beam is rotated and which is modulated in synchronism with its rotation about the transmitter position. The modulation of the beam is such that continuous indications may be had from an indicator at the receiver station in contrast to indications by azimuth segments as in In order .that the bearings obtained with such a system remainy independent of supply voltage changes or input or output signal changes and so forth, the transmitter signals are maintained in the form of ratios rather than absolute signal values. By this means the accuracy of the system may be maintained independent of the operating parameters at either the transmitter or the receiver.

It is an object loi my invention to provide for an omni-directional radio beacon system of the above-mentioned type, apparatus suitable for transmitting signal ratios from which directional information may be obtained by a. receiver.

It is also an object of my invention to provide for a radio beacon system a transmitter in which having a given first frequency and varying as the sine, a second signal having another given frequency and varying as the cosine, of the angle of rotation of the transmitter antenna, and a third signal having a third given frequency which'has a constant amplitude, A This may beobtained by applying the rst signal to the modulating effect of a variometer, the rotary coil of which rotates in synchronism with the rotating antenna of the transmitter and producing thereby a signal whose amplitude varies sinusoldally with the rotation, as described in detail hereinbelow'. This azimuth modulated signal together with the unmodulated signal obtained directly is applied to an adding circuit resulting in a signal which varies from a minimum to a maximum value and back to the minimum value with the complete rotation of the antenna.

A similar signal component is obtained from a second oscillator. In this case, however, the output of the variometer is made to vary as a cosine function. The output of a third oscillator remains at constant amplitude independent of the rotating antenna and is applied together bined with a further constant amplitude signal to render these varying amplitude signals at the receiver point usable to produce indications in 360 degree angles.

Itis a still further object of this invention to provide in a transmitter of the above defined type circuit means for combining two component varying amplitude signals.

Still another object is to provide in a transmitterwherein three component signals are combined, circuit means for regulating the relative phase and volume of at least two of the combining signals to obtain a properly matched combination of the component signals.

According to a feature of this invention, a beacon transmitter when usedwith a cross coil ratiometer indicator at the receiver, as contemplated in the above-mentioned copending application, requires a modulating composite signal varying in time according to the sum of a signal with the previous two component, signals to a common mixer device. Thus the output of the transmitter modulating unit consists of a composite signal made up of the three signals withA different frequencies at constant amplitude and of two components having amplitudes varying in accordance with a sine and a cosine function respectively. The output of the modulating unit contains all the information necessary for indicating the bearings of a receiver which may be on a ship or plane. This composite signal may be applied directly to modulate the transmitter.

The variation in amplitude of two of the audio frequency signals is effected, as hereinbefore stated, by a variometer driven mechanically in synchronism with the transmitter antenna. The variometer has two stator coils physically disposed at an angle of to each other and one rotary coil. Due to the physical positions of the two stator coils, the amplitude variations induced in the rotary coil are 90 out-of-phase, that is, one is a sine function and the other a cosine function o the rotary angle. The signals of varying amplitude obtained from the rotary coil and the currents of fixed amplitude obtained from the inputs to the stator coils are added in a mixing resistor to provide the required composite of the fixed and the sinusoidally varying amplitudes. Due to the fact vthat any voltage supplied to the stator coils will be somewhat out-of-phase with respect to the voltages induced in the rota'ry coil, phase adjustment controls have been provided: to overcome any discrepancy oi' that sort. Td attain accurate composite sine and cosine functions, voltage amplitude regulators have also been provided for the two voltages, components of which are to be varied in amplitude.

These and other features and objects of my invention will be better understood in connection with the detailed description of the drawing, in which the single figure represents, partly in block and partly in schematic form, the circuit diagram of a beacon transmitter incorporating my invention.

'Ihe transmitter is shown to comprise three oscillators I, 2 and 3 producing signals at frequencies F1, Fi, and Fa, respectively. These signais may be amplified in the respective amplifiers ai, 5 and 8 and from there applied to energize automatic volume control circuits 1, 8 and 9 which, as disclosed in my copending application L, Dubin (3), Ser. N0. 586,225, filed April 2, 1945, y

which iSsuedAugust 5, 1947 as Patent No, 2,424,- 972 serves to preserve the stability oi the oscillator outputs. The signal voltages oi the first and second oscillators, as obtained from amplifiers and 5, are fed to stator coils lil and ii of a variometer I2. A rotary coil of the variometer I2 is indicated at I3. The inputs to the two stator coils are subjected to an adjustment in phase by means of a phase adjustment control comprised of a condenser III and resistors I5 and i6 in series therewith to ground at I1. Resistor I6 is shown to be adjustable to permit a variation in phase of the output voltage of the oscillator I. In order to be able to vary the oscillator output voltage with respect to that of the other two oscillators a resistance circuit comprising a resistor I8 and a potentiometer I9 in parallel with the resistors I5 and IB has been provided. .A similar circuit including ya phase adjusting circuit comprising a condenser 2U, resistors 2i and 22 and an oscillator voltage regulating circuit comprising resistor 23 and a potentiometer 2i grounded at 2li are supplied for the second oscillator 2. In order to attain the composite modulating signal as required, the various signal components are combined in a mixing resistor 26. To reduce loading of each voltage source by the combined impedance of all other circuits. to reduce the voltage drop across each coil due to currents of all other voltage sourcesand to reduce the effects of variation of the impedance of the stator and rotary coils due to various positions of the rotary co'il, each voltage source is connected to the mixing resistor 26 through an individual series resistor which is preferably high compared with the voltage source impedances. The signal output of the rotary coil I3 which combines the two varying amplitude components is applied to the mixer 26 through a resistor 21. The phase and amplitude-adjusted voltage output of the first oscillator, which at this point is of fixed amplitude, is fed to the mixer through a resistor 28, the analogous output of the second oscillator being fed through a resistor 29. The output signal component of the third oscillator is fed directly at constant amplitude to the mixlng resistor 26 through a series resistor SII.

To bring the resultant composite signal up to the value required and to match a given load impedance, a cathode-follower stage is used between the mixer 26 and output terminals 3i. The cathode-follower stage comprises 'an amplifier tube 32, the grid of which is coupled to the mixer 2B by means of a coupling condenser 33, The

tube 32 is biased by a grid resistor 84. and a cohdenser and resistor SB in its cathode circuit, A cathode-follower resistor 38 which may be in the form of a potentiometer serves as an output level control for the composite signal. Ihis composite signal may then be applied as a modulating voltage to a transmitter 31 provided with an antenna 82 which is rotated in synchronism with therotary coil il.

In order to improve the stability of operation of the oscillator circuits and to preserve the signal ratios, automatic volume control circuits l. and 9 are preferably given a common bias from a B+ voltage supply at 3B which also serves to provide the plate potential for the three oscillators.

In operation, the constant amplitude signal output S of the three oscillators may be expressed as follows:

S14-.A sine (21rFit) S2=A sine (21rF2t) Sa=A Sine (21rF3t) for the three respective oscillators. As the rotary coil I3 rotates past the two stationary coils i0 and II, it has induced therein two voltages due to the stator coil fields, which vary in amplitude sinusoidally with the rotation thereof. As already defined above. the relative degree angularity of the two stator coils causes the two induced voltages in the rotary coil to Abe 90 outof-phase. that is, one to be a sine and the other a cosine function of the rotary or azimuth angle. The rotary coil is therefore acting to combine the two varying amplitude signals which are applied in their combined form to the series resistor 2l in the mixer circuit. The expressions for the two amplitude varying components in the rotary coil may be represented in this form:

B sine 0 (A sine 2arFit) due to the first and B cosine 0 (A sine 21rFat) due to the second oscillator. sions, B is the maximum amplitude of the voltage developed in the rotary coil and 0 is the antenna azimuth angle.) The sum of these two signals is available in the adding circuit represented by the resistor 21. The other resistors 2t, 29, and 30 of the adding circuit serve to add to this the three constant amplitude signal components as originally generated by the oscillators and as adjusted in the phase and amplitude control circuits for oscillators I and 2.

In order to obtain accurate composite sine and cosine functions, the fixed amplitude and the variable amplitude current components for each frequency must be in exact phase. To overcome the effect of the coil resistance which will effect a slight phase shift of the voltage induced in the rotary coil with respect to that of the stator coil, the fixed amplitude component is obtained over the phase adjusting circuit as described above, consisting of the condenser Id, the resistor I5 and the adjustable resistor i6. By proper adjustment of the respective phase, the stator voltages may be brought into phase with the corresponding rotary voltage. The resistor le is connected in such a way as to prevent the adjustment of' circuit I5 and I6 down to zero in order to avoid a short-circuiting of the input voltage to ground.

In addition to the phase adjustment, the xed amplitude and the maximum value of the varying amplitude for each frequency signal must be adjusted so that the latter at most is equal to or (In these expresless than the former if desired sine and cosine functions are to be obtained. The relative amplitude of the currents in the rotary and the stator coils is dependent on the ratio of the turns of the coils which may be for instance l/N. A possibility for adjusting the relative amplitudes is therefore provided so as to adjust the fixed amplitude current to approximate the desired ratio with respect to the maximum value of the varying amplitude current. The resistances i and I9 connected in parallel with resistors i and i6 serve this purpose'by means of the adjustability of the resistance i9. Similarly the resistors 23 and lit serve an analogous purpose for the second oscillator. The ratio of adjustment in the potentiorneters i9 and 2t, is proportional to the turns ratio, that is, l/N, and will result in a possible Variation of the fixed amplitude signal from an amplitude of zero to l/N of the stator voltages.

The three fixed amplitude and the two varying amplitude signals are then combined in the resistor 26 through their respective series resistors El thru 3d. The mixing resistor 26, across which the composite modulating output voltage may be obtained, is preferably high compared to that of the series resistors, in order to utilize a large portion of the developed voltage for the output. Assuming that all the fixed amplitudes and the maximum values of the varying amplitudes are adjusted to the same value A and that all signals add in phase, the sum of the five amplitudes may be expressed as follows:

A(1 +sine 0 l -i-cosine -9-4-1) Before the adjustment of the component signals, the composite is the sum of the following:

(A4-AB sine 0) sine (21rF1t) (A4-AB cosine 9) sine (21rF2t) and Ai sine 2 Fat (where B is a fraction of A, depending on the turns ratio of the coils, but of course having a predetermined desired value).

It will be understood from the above, that in the description, when the quantity A is used to denne the amplitude of one of the signals, the final, that is, the value of the amplitude after adjustments, is meant.

For cooperation with this beacon transmitter there is provided, as disclosed in the copending application of E. Labin, et al. (Q2-104), Ser. No. 581,974, filed, March 10, 1945, a radio receiver unit which will receive and detect the radio beam energy. In the output of the receiver-detector unit the three signals are then separated and applied to subtracting circuits for removing the envelope of the constant amplitude signal from the two variable amplitude signals. As a result there will be two output energies, one proportional to the sine function and the other proportional to the cosine function. These two energies may then be applied to a ratiometer to measure the ratio of the energy received thereby producing an indication of direction.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects of my invention and the accompanying claims.

I claim:

1. In a directionally shiftable radio beacon transmitter, a source of unmodulated signal havamplitude of said signal in accordance with the directional shift of said beacon, and means for mixing said unmodulated signal with the output of said last named means.

2. In a directionaily shiftable radio beacon transmitter, a source of unmodulated signal having a given frequency, a variometer for modulating the amplitude of said signal including a coil rotated in synchronism with the radiation pattern of the transmitter antenna, and means for mixing said unmodulated signal with the output of said last named means.

3. In a directionally shiftable radio beacon transmitter, a source of unmodulated signal having a given frequency, means for modulating the amplitude of said signal in accordance with the directional shift of said beacon, two output resistors, one for said signal and one for said last named means, and a resistor for mixing said unmodulated signal with the output of said last named means in series with said two output resistors.

4. A transmitter in accordance with claim 3, further including an amplifying cathode-follower type output stage following` said last-named resistor.

5. In a directional shiftable radio 'beacon transmitter, sources of two unmodulated component signals having a first and a second frequency respectively, means for combining said two signals with their amplitude ratios varying in accordance with the directional shift of said beacon, and means for mixing at least one of said unmodulated signal components with the output of said means-for-combining.

6. A transmitter in accordance with claim 5,

wherein said rst named means comprises a variometer having a coil rotated in synchronism with the radiation pattern of the transmitter antenna.

'1. A transmitter in accordance with claim 5, wherein said means for mixing comprises a resistor for the output of said means-for-combinlng and one resistor each for said two signal sources, and an output mixing resistor in series with each of the other resistors.

8. A transmitter in accordance with claim 5, further including an amplifying cathode-follower type output stage.

9. A radio beacon transmitter, comprising sources of unmodulated component signals having a first, a second and a third frequency respectively, means for combining said first and second frequency signals with their amplitude ratios varying in accordance with the directional shift of said beacon, and means for mixing the output of said means-for-combining with said unmodulated iirst, and third component signals.

10. A transmitter in accordance with claim 9, wherein said first named means comprises Aa variometer having a coil rotated in synchronism rwith the radiative pattern of the transmitter antenna.

11. A transmitter in accordance with claim 9, wherein said means for mixing comprisesa resistor foi` the output of said means-for-combining and one resistor each for said three signal sources, and an output mixing resistor in series with the other resistors.

12. A transmitter in accordance with claim 9, further including an amplifying cathode-follower type output stage.

13. In a rotary beacon transmitter, the combination comprising means for producing a signal having a given frequency, a second means for ing a given frequency, means for modulating the w 'Producing a signal having anthr' given freainsi fluency. and rotatable coupling means for combiningsaid ilrst and second signals in a manner to give said two signals a modulation in accordance with a sine and a cosine function respectively.

14. 'I'he combination in accordance with claim 13, wherein said means for combining comprises a variometer having two stator coils and one rotary coil, said two signals being applied to said two stator coils respectively.

15. A rotary radio beacon transmitter for producing a composite signal containing component signal functions of (A+sine and (A-i-cosine 0) where 0 is the rotating'radiation pattern azimuth angle, comprising respective sources for producing signals having a first, a second and a third frequency, means for combining the first and second signals to sive said first and said second signals a modulation in accordance with a sine and a cosine function respectively, means for mixing with the output of said means-forcom'bi'ning said unmodulated rst, second and third component signals, and means for controlling the application to said mixing means of the unmodulated iirst and second signals with respect to the corresponding modulated components to produce a resultant siunmation.

16. A transmitter in accordance with claim 15, wherein said means for controlling includes a phase adjuster for said :ilrst and said second signals. whereby in-phase mixing oi the component signals is obtainable.

17. A transmitter in accordance with claim 15, wherein said means for controlling includes an amplitude adjuster for each of said two signals, whereby the maximum amplitude of the modulated components and the amplitude of theunmodulated components may be equalized.

18. In a directional shiftable radio beacon transmitter which comprises respective sources for producing a plurality of signals having given frequencies, means for producing a summation of signal components modulated in accordance with the directional shift of said beacon of a group of said plurality o! signals with the unmodulated components of another group of said signals: the means for controlling the phase of the unmoduiated signals, the components oi which have been modulated, with respect to said corresponding modulated components: and means for controlling the voltage amplitude oi' said same unmodulated signals.

19. Means for controlling the phase and means for controlling the voltage amplitude in accordance with claim 18, wherein said rst named means comprises a condenser and an adjustable resistor circuit in series therewith to ground and wherein said second named means comprises in said condenser a potentiometer circuit to ground.

REFERENCES CITED The following references are of record in the ille of this patent:

UNrrED s'rA'rEs PATENTS Number 

